The present invention relates to a new and improved construction of an inertial sensor arrangement.
The present invention specifically relates to a new and improved inertial sensor arrangement of the type as described in prior U.S. patent application, Ser. No. 08/797,162, filed Feb. 10, 1997, and which comprises an inertial sensor operating by utilizing the SAGNAC-effect. Such inertial sensor responds to the horizontal component of the angular rate of the earth and can be rotated about a vertical axis into a multiple number of fixed positions. Signals obtained thereby are processed through signal processing means in order to form a measured value representing the angle formed between a reference direction and north. The inertial sensor of the inertial sensor arrangement comprises a fiber gyro mounted at a positioning frame which is supported for rotation about a vertical axis relative to a housing. Adjusting means are provided for rotating the positioning frame into three fixed positions and locking means are provided for locking the same in the three fixed positions. Inclination sensors, which define intercrossing sensitive axes, are provided for determining the inclination of the inertial sensor arrangement relative to the horizontal.
In the construction described in the aforenoted prior U.S. patent application the signal processing means are formed by printed circuit boards which are provided with electronic components and which constitute the bottom and side walls of a rectangular inner housing. A positioning frame protrudes through the bottom into the inner housing and is rotatably supported therein by means of a bearing arrangement. A fiber gyro including a fiber coil is supported at the positioning frame. The positioning frame can be rotated about a vertical axis relative to the inner housing by means of a servo motor into three fixed positions which are defined by mechanical locking means. The input axis of the fiber gyro is inclined by an elevational angle relative to a plane which extends perpendicular to the vertical axis. An outer housing is open at its bottom and placed on top of the inner housing. Two accelerometers, which define respective, mutually substantially perpendicular sensitive axes, are fixedly mounted at respective printed circuit boards which form the side walls of the inner housing.
In the arrangement according to the aforenoted prior U.S. patent application, the accelerometers are mounted at the inner housing formed by the printed circuit boards. The fiber gyro is placed at the rotatably supported positioning frame. Due to thermal effects caused by the heat originating from the electronic components mounted at the printed circuit boards, slight distortions may occur at the printed circuit boards. Such distortions affect the relative positions of the accelerometers versus the fiber gyro. As a consequence, the measurement is adversely affected because the orientation of the fiber gyro relative to the horizontal is determined by the accelerometers.